Respiratory delivery systems, such as metered dose inhalers, dry powder inhalers, and nebulizers, generally make it possible to introduce substances to pulmonary tissue of the body usually via simple inhalation. Metered dose inhalers generally combine a medicament and a propellant in a pressurized aerosol container equipped with valve to release a metered dose of aerosol into an inhaled airstream upon actuation of the container. Dry powder inhalers usually utilize bursts of inspired air to fluidize powdered doses of medicament and draw these powdered doses into the respiratory tract. Nebulizers generally form an aerosol by atomizing a medicament in a substantially continuous carrier gas stream which can then be inhaled.
Regardless of the respiratory delivery system utilized, conventional introduction of medicament to the pulmonary tissue of the human body has much to be desired in the way of successfully delivering a selected/predetermined amount of medicament to the pulmonary tissue of an individual regardless of the relative strength/weakness of that individual's respiratory system. For example, current metered dose inhalers generally require at least some synchronization between valve actuation and the user's inhalation (which has proven difficult for some users). Since metered dose inhalers generally depend on a minimum threshold inhalation by the user, an inhalation which is below that minimum threshold can result in less than the required amount of medicament successfully reaching the pulmonary tissues. Accordingly, various attempts have been made to develop metered dose inhalers which “sense” the amount of airflow during inhalation and vary the amount of drug dispensed based on the flow rate of the inhalation. In other words, in an exemplary situation in which two individuals utilize metered dose inhalers equipped with such “sensors”, a first individual (who can inhale with less strength than a second individual) will have a greater concentration of medicament dispensed with every actuation than the second individual will have. However, such attempts at regulating amounts of medicament to depend on the strength of the user's inhalation have resulted in varying degrees of success, all of which tend to provide a hefty price tag for the consumer.
Dry powder inhalers at least generally tend to avoid the synchronization problem of metered dose inhalers. However, dry powder inhalers also fail to solve the problem of varied magnitudes of inhalation from user to user, and (regarding the same user) from situation to situation. In other words, an individual may not be capable of effecting an inhalation that has enough force to “fluidize” and inspire the entire amount of powdered medicament. Accordingly, the dose(s) of powdered medicament which actually reaches the pulmonary tissue tends to vary based on the force of inspiration.
As for nebulizers, inhalation generally tends to reduce pressure at the nebulizer nozzle; accordingly, the desired dosage of medicament is generally influenced by the duration and strength of the user's inhalation. While most nebulizers function on a “continuous stream of vapor” basis, control systems have been utilized to direct the aerosolized gas flow from the nebulizer to a “holding chamber” from which the user may draw a charge. However, these “charges” are still generally dependent upon a user being able to inspire the entire amount of vaporized medicament from the holding chamber. Accordingly, a user having relatively weak inhalation capabilities may not receive the entire “charge” of medicament. Thus, varying degrees of success have also been observed with regard to nebulizers that attempt to control the amount of dispensed medicament with respect to a user's inhalation strength.
In summary, the precision of dose delivery in conventional respiratory delivery systems is undesirably imprecise. In each of the above-discussed systems, the desired amount of medicament to be delivered to the intended pulmonary tissue is generally dependent (at least to some degree) on the user's strength of inhalation, and is generally variable from dose to dose and/or person to person. In other words, a correlation has been allowed to exist between a user's lack (or variation) of breathing capability and a lack (or variation) of that user consistently receiving the adequate, prescribed, and/or desired amount of medicament. Accordingly, it would be desirable to develop an improved respiratory delivery system that exhibits effective entrainment of a non-varying amount of dispensed medicament into the airstream and successful delivery of such a non-varying amount of dispensed medicament to the target pulmonary tissue.